1. Field of the Invention
The present invention relates to a sealing member for a fuel cell, and more particularly relates to the sealing member which can enhance sealing performance.
2. Description of the Related Art
There is a per se known type of solid polymer electrolyte type fuel cell which has been developed, in which a plurality of fuel cell units are layered together, each fuel cell unit including a solid polymer electrolyte membrane with an anode electrode and a cathode electrode sandwiching it from its opposing sides, and with a pair of separators sandwiching this membrane electrode assembly having aforementioned structure from both its sides, the whole being secured together into a unit. These fuel cells are effective for various uses.
With these types of fuel cell, fuel gasxe2x80x94for example, hydrogen gasxe2x80x94is supplied to the anode electrode side, and is converted into hydrogen ions by an electrode catalyst, and then moves towards the cathode electrode via the solid polymer electrolyte membrane which is appropriately humidified. The electrons which are generated at the anode are emitted to an external circuit, and are used as DC electrical energy. An oxidizing gas, for example oxygen gas or air, is supplied to the cathode electrode, so that these hydrogen ions, this oxygen gas, and these electrons are reacted together at this cathode electrode to generate water.
Moreover, gas-tightness is ensured by the provision of sealing members between separators which are provided on both sides of the membrane electrode assembly, in order for this fuel gas and oxidizing gas which are supplied to the anode electrode and the cathode electrode not to leak to the outside, and it is arranged for the fuel gas and the oxidizing gas to be conducted to the reaction surfaces, which are the portions of these separators which are introduced by the sealing members.
Furthermore, in order to prevent rise of the temperature of the fuel cell due to the reaction between the fuel gas and the oxidizing gas, a coolant fluid is supplied to between neighboring ones of the separators when the fuel cell units are layered together, and sealing members are provided for preventing leaking out of the coolant fluid to the exterior around the peripheries of the cooling surfaces of the separators, as well.
In addition, when supplying the reaction gases such as fuel gas and oxidizing gas to the anode electrode and to the cathode electrode, and supplying coolant fluid to the cooling surfaces, if an internal manifold structure is used reaction gas supply holes (or openings)and coolant supply holes are formed to penetrate through each separator, it is furthermore necessary to seal the periphery of each supply hole with a sealing member.
An example of a prior art such sealing member which surrounds the reaction surfaces will now be explained with reference to FIG. 11. In FIG. 11, reference numeral 1 denotes the solid polymer electrolyte membrane, and this solid polymer electrolyte membrane 1 is sandwiched between an anode electrode 2 and a cathode electrode 3, to constitute a membrane electrode assembly 4. This membrane electrode assembly 4 is further sandwiched between a pair of separators 5 and 6 on both its sides, and constituting the fuel cell.
The periphery of the solid polymer electrolyte membrane 1 extends further outwards than the peripheral edge portions of the electrodes 2 and 3, and this projecting edge portion is sandwiched on both its sides by sealing members 8 which are fitted into grooves 7 formed upon the inwardly facing surfaces of the separators 5 and 6. And reaction gas conduits 9 and 10 are formed in the surfaces of the separators 5 and 6 which face the electrodes 2 and 3.
Accordingly, fuel gas and oxidizing gas are respectively supplied to the reaction gas conduits 9 and 10 defined between the electrodes 2 and 3 and the separators 5 and 6 which are surrounded by the above described sealing members 8, and the sealing members 8 ensures that these reaction gases do not escape to the outside. This matter is disclosed in Japanese Patent Application, First Publication No. Hei 8-37012.
However, with the sealing member for a fuel cell according to the above describer prior art, when the sealing member 8 is affixed by being pushed into the groove 7 until the width of the groove 7 is filled, and the separators 5 and 6 are fitted to both sides of the membrane electrode assembly 4 and are fastened thereagainst by being clamped, since there is no space into which the deformed sealing member can be released, a great fastening force for the clamping mechanism is necessary, and the surface pressure upon the sealing member 8 becomes great. Accordingly, the problem arises that a clamping mechanism of relatively great size and weight is required for ensuring a sufficiently great clamping force, when a plurality of these fuel cell units are layered together into a fuel cell assembly.
By contrast, it would also be possible to make the width of the groove 7 relatively large with respect to the diameter of the sealing member 8 which is to be used, and to fit the sealing member 8 into the groove 7 with a degree of extra space being left available. However, if this is done, when the separators 5 and 6 are clamped against the membrane electrode assembly 4 from both its sides, positional deviation or slippage of the sealing members 8 in the grooves 7 of the separators can easily occur, as shown in FIG. 12, and thus the problem arises that it is not possible to ensure a reliable seal between the separators 5 and 6 and the solid polymer electrolyte membrane 1, due to the shearing force which can deform the solid polymer electrolyte membrane 1.
It is the objective of the present invention to provide a sealing member for a fuel cell, with which it is possible to keep the surface pressure which is applied to the sealing member low, thus making it possible to enhance the sealing performance.
In order to achieve the above described objective, the first aspect of the present invention proposes a sealing member (for example, in the disclosed embodiment, the sealing members S1 and S2) for a fuel cell which comprises a pair of electrodes (for example, in the disclosed embodiment, the anode electrode A and the cathode electrode C) which sandwich an electrolyte membrane (for example, in the disclosed embodiment, the solid polymer electrolyte membrane 15) on both its sides, and a pair of separators (for example, in the disclosed embodiment, the anode side separator 13 and the cathode side separator 14) which sandwich the electrolyte membrane on both its outer sides. The sealing member installed into a groove (for example, in the disclosed embodiment, the grooves 38 and 39) in each separators, and characterized by being formed, in cross section, with a pair of cutaway portions (for example, in the disclosed embodiment, the cutaway portions 43) in symmetrical positions with respect to the center of a chord portion (for example, in the disclosed embodiment, the chord portion 40b) of a generally semicircular shaped sealing member main body (for example, in the disclosed embodiment, the sealing member main body 40).
According to the sealing member having this structure, when pressure acts from the arcuate portion (for example, in the disclosed preferred embodiment, the arcuate portion 40a) which opposes the chord portion of the sealing member main body, the portion between said pair of cutaway portions becomes a sealing surface (for example, in the disclosed preferred embodiment, the bottom portion 40c), and it is possible to enhance the sealing performance. Furthermore, it is possible to ensure a relatively large amount of elastic deformation of the sealing member main body with a relatively small amount of pressure, since it is possible to release the portions which have been deformed by the pressure into the void portions (for example, in the disclosed preferred embodiment, the void portions 45) which are defined between the groove and the cutaway portions. Accordingly, if a plurality of these fuel cells are layered together into a single assembly, it is possible to reduce the overall force which is required for clamping them together as compared with the prior art, and thus it is possible to reduce the overall size and weight of the clamping structure.
The second aspect of the present invention proposes the sealing member as described above, further characterized in that projecting portions (for example, in the disclosed embodiment, the projecting portions 42) are provided on both sides of the chord portion extending in the widthwise direction of the groove, and the projecting portions extend to positions which adjoin or contact side walls (for example, in the disclosed embodiment, the side walls 38a and 39a) of the groove.
According to the sealing member having this structure, it is possible to position the central portion of the chord portion at the central portion of the groove in its widthwise direction, and it is possible to ensure that no slippage occurs in the widthwise direction of the groove, since the movement of the ends of these projecting portions which are provided as extending in the widthwise direction of the groove are prevented by the side walls of the groove.
And the third aspect of the present invention proposes the sealing member as described above, further characterized in that cutaway portions (for example, in the disclosed embodiment, the cutaway portions 44) are formed upon the projecting portions at predetermined intervals in the lengthwise direction of the groove.
According to the sealing member having this structure, when pressure acts upon the arcuate portion, it is possible to ensure a relatively great amount of elastic deformation, since it is possible to release the portions which are deformed into the void portions (for example, in the disclosed preferred embodiment, the void portions 45) which are defined between the side walls of the groove and the cutaway portions. Moreover, the ease of working when inserting the sealing member into the groove is enhanced, because the area of the projection portion which contacts the groove is reduced.